Vendor import of clang release_90 branch r371301:vendor/clang/clang-release_90-r371301

https://llvm.org/svn/llvm-project/cfe/branches/release_90@371301

1 files changed, 19 insertions, 4 deletions

diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 468c7f47657d..93bdaafc2ac6 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -9814,10 +9814,25 @@ static GVALinkage basicGVALinkageForVariable(const ASTContext &Context,
     return StrongLinkage;
 
   case TSK_ExplicitSpecialization:
-    return Context.getTargetInfo().getCXXABI().isMicrosoft() &&
-                   VD->isStaticDataMember()
-               ? GVA_StrongODR
-               : StrongLinkage;
+    if (Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+      // If this is a fully specialized constexpr variable template, pretend it
+      // was marked inline. MSVC 14.21.27702 headers define _Is_integral in a
+      // header this way, and we don't want to emit non-discardable definitions
+      // of these variables in every TU that includes <type_traits>. This
+      // behavior is non-conforming, since another TU could use an extern
+      // template declaration for this variable, but for constexpr variables,
+      // it's unlikely for a user to want to do that. This behavior can be
+      // removed if the headers change to explicitly mark such variable template
+      // specializations inline.
+      if (isa<VarTemplateSpecializationDecl>(VD) && VD->isConstexpr())
+        return GVA_DiscardableODR;
+
+      // Use ODR linkage for static data members of fully specialized templates
+      // to prevent duplicate definition errors with MSVC.
+      if (VD->isStaticDataMember())
+        return GVA_StrongODR;
+    }
+    return StrongLinkage;
 
   case TSK_ExplicitInstantiationDefinition:
     return GVA_StrongODR;